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Despite using https://en.bildelsbasen.se things weren’t Utan anmärkning as described.

We found some engine parts filled with water (which by the way means the generator no longer works so we took it from the old engine). It was also very clean : not a single stain.
As if the whole engine was plunged in water in order to be cleaned. (though outside and internals were dry).

The engine starts but with a lot of water smoke and coolent level is decreasing. Compression is 30% below normal for the top left cylinder to 90% below normal for the top right cylinder (each cylinder has compression lower than the previous one).

So looks like head gasket is damaged (though even after running 5 minutes temperature stay cool). If it’s just that, it might worth to buy a new one for 50€, but if a piston ring is damaged, it would cost over 500€ in parts to replace it (which means changing the engine again would be a better idea).

So how to check for damaged piston ring in such situation in order to avoid spending over 200€ for removing cylinder head ?

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  • Most engines have 2 compression rings, both would have to be compromised to cause 30% loss, I suspect it is a head gasket. Sounds like a lemon to me.
    – Moab
    Commented Oct 10, 2019 at 15:31
  • @Moab the point here is compression doesn’t means anything. Also the smoke isn’t blue at all. Though oil level or texture isn’t changing (it’s 5W30 oil).
    – user2284570
    Commented Oct 11, 2019 at 3:14

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You've done the correct first check with a compression test which has shown that there is some problem. But there are multiple causes for low or uneven compression:

  1. Damaged piston ring and/or damaged cylinder wall
  2. Bent, burnt, or stuck valve
  3. Damaged piston
  4. Blown head gasket
  5. Cracked head or block

There are likely other causes which are not coming to my mind right now. The next step short of removing the cylinder head might be a borescope inspection which may show something additional about the cylinder in question.

But I think that ultimately you will need to pull the head to conclusively diagnose the problem. That, of course, may be more than you want to spend on this problem. If, for example, you know that the rings are damaged and the cylinder wall is scored, a total rebuild is the only solution it may make more sense to replace the engine with a used or remanufactured one than to repair the existing one.

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  • @Moab That depends on just how bent, stuck, or burned it is. In the impact could be anywhere from 100% compression loss to nearly none at all.
    – jwh20
    Commented Oct 10, 2019 at 16:35
  • You need to add "burnt" to you answer.
    – Moab
    Commented Oct 10, 2019 at 16:46
  • My mechanic, nor I have a borescope. So without a borescope was the point of the question.
    – user2284570
    Commented Oct 11, 2019 at 3:10
  • 1
    Find a better mechanic who has the proper tools for the job or buy a borescope for yourself.
    – jwh20
    Commented Oct 11, 2019 at 9:20
  • Decent quality borescopes are getting relatively cheap. Even if you don't want to get one, perhaps it's time for your mechanic to get one... Handy for so many things.
    – Brian Knoblauch
    Commented Oct 11, 2019 at 16:07

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